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Network Layer

Network Layer. We have discussed data link architectures CSMA/CD Point-to-Point Wireless LANs These architectures deliver frames to next station They implement network segments, possibly connected through bridges One might build a private medium size private network this way

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Network Layer

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  1. Network Layer • We have discussed data link architectures • CSMA/CD • Point-to-Point • Wireless LANs • These architectures deliver frames to next station • They implement network segments, possibly connected through bridges • One might build a private medium size private network this way • Could not build a universal or public network this way

  2. Network Layer • We would like to interconnect such networks into a consistent larger network • We could consider this larger network an internet, an interconnection of networks • Logical ‘gluing’ of heterogeneous layer 2 networks to appear as a single network • A number of issues must be addressed • Universal addressing • Routing • Packetizing data

  3. Network Layer Addressing Routing Packetizing CSMA/CD IEEE802.3 IEEE 802.11 Pt-to-Pt HDLC PPP Physical Layer Twisted pairs Fiber Optics encoding Network Layer

  4. Network Layer • There are and have been many network layer protocols • Systems Network Architecture (SNA) – IBM • DECNET – Digital Equipment Corporation • OSI – International Standards Organization • AppleTalk – Apple Computer • Internetwork Packet Exchange (IPX) – Novell • Internet Protocol (IP) • Each of these has its own addressing scheme • Each has own packet format • Each implements own versions of routing

  5. Network Layer • We will discuss the Internet Protocol • Recall, this is layered protocol, much like the OSI model • Internet Protocol does not have its own physical or data link layers • Uses existing lower layer protocols as discussed • The Internet Protocol is often called TCP/IP which represents its two underlying protocols

  6. Comparison of OSI and TCP/IP Data Link Physical

  7. Internet Protocol Historical Summary • 1969 – Four node ARPANET established • 1973 – Development of TCP/IP suite begins • 1978 – UNIX distributed to academic sites • 1981 – CSNET established • 1983 – TCP/IP becomes official protocol • 1983 – NSF funds a national backbone linking 6 supercomputer centers • Emerging regional networks link to backbone nodes • Initial backbone 56Kbps

  8. Internet Protocol Historical Summary • 1987 – NSF backbone increased to T1 • Partnership formed to operate NSFnet • Merit – Michigan • IBM • MCI • 1991 NSFNET backbone increased to 45 Mbps • 1993 – NSFNET establishes migration to a commercial Internet • 1995 – Internet Service Providers (ISPs) established

  9. Internet 2 • Established in 1998 • Separate physical network for research institutions • Uses same Internet Protocol • Network Operations Center (noc) at Indiana University • Core Network called Abilene • Circuits provided by Qwest Communications

  10. Abilene Access Nodes Seattle Cleveland Sacramento New York Denver Indianapolis Kansas City Los Angeles Atlanta Abilene Core Node Houston Abilene Access Node Operational January 1999

  11. Internet today

  12. Internet Standards Bodies Internet Society(ISOC) http://www.isoc.org Internet Architecture Board (IAB) http://www.iab.org Internet Research Task Force (IRTF) http://www.irtf.org Internet Engineering Task Force (IETF) http://www.ietf.org Internet Protocols Routing Management

  13. Internet Standards Documentation • Official standards published in documents called Request for Comments (RFCs) • RFCs go through various stages • Internet Draft • Experimental • Informational • Proposed standard • Draft Standard • Internet Standard • RFCs are stored in a public repository http://www.ietf.org

  14. Internet Addressing • For an Internet, we need universal identification of nodes • Must apply to different types of networks • Must be independent of vendor, hardware, physical network • In TCP/IP we deal with various addresses • Physical addresses – MAC addresses • IP addresses – universal address • Port – specifies service

  15. Internet Addressing • Administration of Internet addresses • Internet Corporation for Assigned Names and Numbers (ICANN) http://www.icann.org • Internet Assigned Numbers Authority (IANA) http://www.iana.org Authorizes and oversees 5 registries • APNIC (Asia Pacific Network Information Centre) • ARIN (American Registry for Internet Numbers) • RIPE NCC (Réseaux IP Européens) • LACNIC (Regional Latin-American and Caribbean IP Address Registry) • AfriNIC (African Network Information Centre)

  16. Internet Address • An IP address is 32 bit word • Maximum of 232 or 4,294,967,296 addresses • Address are assigned in ranges to accommodate • Large networks • Medium size networks • Small networks • Convenient to break address into two parts • Range number – network • Individual numbers within the range - host

  17. 0 8 31 0 netid hostid 1 0 netid hostid 31 0 1 16 Internet Address Address space originally defined into classes Class A - Maximum 128 Class A networks - Each network could have 224 or 16,777,215 addresses or hosts Class B - Maximum 16,384 Class B networks - Each has 65,536 addresses or nodes Net id = 0 - 127 Net id = 128 - 191

  18. 1 1 0 netid hostid 0 31 24 1110 multicast 0 31 11110 future 0 31 Internet Address Net id = 192 - 223 Class C - Maximum 2,097,152 Class C networks - Each network has 28 or 256 addresses Class D Class E Net id = 224 - 239

  19. Netid and hostid

  20. Internet Addresses • It is common place to represent a 32 bit Internet address in dotted notation • Given a 32 bit address 0x826F27A2 We would write as 130.111.39.162 • Here 130.111 is the network address 39.162 is the host id • The address in this network range 130.111.0.0 to 130.111.255.255 • Likewise, the 193.56.120.50 is part of the range 193.56.120.0 to 193.56.120.255

  21. 0’s hostid 127 Anything Special Internet Addresses • By convention 0 means ‘this’ 1 means ‘all’ All 0’s This host Host on this network Loopback Address Data sent to this address is returned Never sent out on network

  22. netid 0s netid 1s 0s 1s Special Internet Addresses Refers to this network (netid) Not assigned to any host All hosts on this network (netid) Called a directed broadcast All host on local network Called a limited broadcast

  23. Addresses and Routing • Devices that determine paths or routing need only know about network addresses • Only the destination network need be concerned about the host address • Devices that determine paths or routes are usually called routers • Routers must have tables entries, called a routing table, for every network in order to determine paths

  24. Subnetting • Some networks (Class A & B) are large enough to warrant breakdown into smaller groups, subnets • An organization may be assigned a large range (Class B) and may wish to allocate to departments in smaller subnets • To make internal routers treat these subnets internally as separate networks requires additional information • Must specify which bits in the address represents the network id

  25. Subnetting • To provide for subnetting addresses are specified in two parts • The address • A mask – indicate which bits make up network address • Example: 130.111.32.150 is part of a class B • We could break this into smaller networks 130.111.32.150255.255.255.0 • 130.111.32 would be treated as a network id and .150 as the host id within that network

  26. Subnetting • Specified in RFC 950 • Examples • 130.111.39.5 255.255.255.0 • 130.111.39.5 255.255.255.128 • 130.111.39.5 255.255.255.192 • 130.111.39.5 255.255.255.224 • 130.111.39.5 255.255.255.240 • 130.111.39.5 255.255.255.252

  27. Subnetting • Alternative notation – Slash notation • Instead of specifying a mask, indicate how many bits constitute the network address • 130.111.39.250 255.255.255.0 • 130.111.39.250/24 • Thus, any Class B network could be specified as a.b.c.d/16

  28. Supernetting • Much like subnetting a Class x network, we can collect adjacent Class x networks to form larger networks • Consider the two Class C networks 193.240.88.0 255.255.255.0 193.240.89.0 255.255.255.0 Each of these is a network of 256 addresses • We could group these into a single network as follows 193.240.88.0 255.255.254.0 193.240.88.0/23

  29. 255.255.0.0 255.255.192.0 141.14.0.0 141.14.64.0 141.14.72.24 141.14.72.24 AND AND Determining Network/Host Address

  30. Defining Subnets • An organization is allocated a Class B network 181.56.0.0 • The organization needs at least 1000 subnets • If a common mask will be used for all these subnets, the number must be a power of 2. • There will be 1024 subnets • The mask will be 255.255.255.192 • Each subnet will have 64 addresses

  31. Network ID Host address (64) Subnet (1024) Defining Subnets 11111111 111111111111111111000000 181.56.0.0255.255.255.192

  32. Defining Subnets • What is the range of the first subnet? • 181.56.0.0 181.56.0.63 • What is the range of the second subnet? • 181.56.0.64 181.56.0.127 • What is the range of the last subnet? • 181.56.255.192 181.56.255.255 • What is the range of the 1023rd subnet? • 181.56.255.128 181.56.255.127

  33. Classfull Addressing • Class A networks are too large which results into wasted address space • Class B are also too large for many organizations • Class C networks are too small, requiring multiple allocations to the same organization • In the early 90s, it became clear that this method of address space allocation would lead to early depletion of addresses

  34. Classless Interdomain Routing(CIDR) • To preserve address space, a new method of assigning space was developed in 1993 • Groups of unassigned address were allocated regionally (RFC 1466) • New allocation scheme provided for allocation of variable length blocks of addresses • Going forward, allocations would no longer be done by Class • Allocation scheme defined in RFC 1518

  35. Classless Interdomain Routing • Address blocks are sized by powers of 2 • Blocks of size 2,4,8,…., 256, 512, 1024… can be assigned • Stating address must be divisible by the number of addresses in the block • The allocation is specified the same fashion as subnets using slash notation • Original allocations are maintained and folded into this scheme • Routers modified to accept and maintain their routing tables in this way

  36. Managing Address Space • Blocks of addresses assigned to ISPs • ISPs assign subnets to customers • Assigned subnets can be of variable sizes • When customers change Service Provider, they usually have to change address space • Usually, the ISP will assign large subnets first, followed by smaller subnets

  37. Variable size Subnetting An ISP is granted a block of addresses starting with 190.100.0.0/16. The ISP needs to distribute these addresses to three groups of customers as follows: Group 1 has 64 customers; each needs 256 addresses Group 2 has 128 customers; each needs 128 addresses. Group3 has 128 customers; each needs 64 addresses.

  38. Variable size Subnetting • Group 1 • For this group, each customer needs 256 addresses. • This means the suffix (host-id) length is 8 • The prefix length (net-id) is then 32 - 8 = 24. • 01: 190.100.0.0/24 190.100.0.255/24 • 02: 190.100.1.0/24 190.100.1.255/24 • ………………………………….. • 64: 190.100.63.0/24190.100.63.255/24 • Total = 64  256 = 16,384

  39. Variable size Subnetting • Group 2 • For this group, each customer needs 128 addresses. This means the suffix length is 7 (27 = 128). The prefix length is then 32 - 7 = 25. The addresses are: • 001: 190.100.64.0/25 190.100.64.127/25 • 002: 190.100.64.128/25 190.100.64.255/25 • ………………………………………. • 128: 190.100.127.128/25 190.100.127.255/25 • Total = 128  128 = 16,384

  40. Variable size Subnetting • Group 3 • For this group, each customer needs 64 addresses. This means the suffix length is 6 (26 = 64). The prefix length is then 32 - 6 = 26. • 001:190.100.128.0/26 190.100.128.63/26 • 002:190.100.128.64/26 190.100.128.127/26 • ………………………… • 128:190.100.159.192/26 190.100.159.255/26 • Total = 128  64 = 8,192

  41. UMS Managed Address Space 130.111.0.0/16 University of Maine System 169.244.0.0/16 Maine School and Library Network 141.114.0.0/16 State of Maine Government 192.43.249.0/24 Jackson Laboratories 198.148.217.0/24 Waterville K12 198.182.161.0/24 State of Maine Government 198.182.162.0/23 State of Maine Government 199.33.141.0/24 College of the Atlantic 207.166.224.0/19 University of Maine System 209.222.192.0/19 University of Maine System 64.45.64.0/18 University of Maine System 65.18.0.0/18 University of Maine System 65.18.64.0/19 University of Maine System 65.18.96.0/20 University of Maine System

  42. Private Addresses • Some organizations want to establish IP networks internally, but not outside the organization • By convention, some address space is allocated for this purpose • These addresses are not accepted (routed) on the Internet, but can be routed internally

  43. Private Addresses • RFC 1918 defines this address space 10.0.0.0 to 10.255.255.255 172.16.0.0 to 172.31.255.255 192.168.0.0 to 192.168.255.255

  44. IP addressing tools Web tool for calculating subnet masks http://library.mobrien.com/index.shtml Tool for calculating subnet masks ipcalc321.exe on course web site (Wildpackets) Tool to look up ownership of IP address space cyberkit - cyber30.zip on web site

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